Multivibrator



March 31, 1959 w. w. SAKS MULTIVIBRATOR Filed July 12, 1957 'E' 2 INVENTOR.

W/AL/AW W \S/ KS A TTOR/VEY United States atent O MULTIVIBRATOR William W. Saks, Bethesda, Md., assignor to Vitro Corporation of America, New York, N.Y.

Application July 12, 1957, Serial No. 671,663

9 Claims. (Cl. 25036) plish this adjustment, the pulse spacing and pulse width I I factors must be so related that an increase in one factor causes a decrease in the other in a manner such that the sum of these factors expressed in time units remains constant.

In conventional multivibrator pulse width adjustment methods, the time constants of the frequency determining coupling networks are suitably adjusted. Such adjustment, for the reasons discussed above, results in an undesirable change in the recurrence frequency of the multivibrator.

The present invention overcomes the former interdependence of pulse width and recurrence frequency controls by connecting two vacuum tubes in parallel circuits and providing switching devices in the anodecathode discharge path of each of the tubes. Suitable circuits coupling the vacuum tube electrodes in a multivibrator arrangement provide free running operation thereof. Such circuits are arranged so that the switching means in the anode-cathode discharge path of each tube responds to current in one tube to shift the control grid of the other tube to a low potential to discharge a capacitor associated with that tube. After a time interval determined by the time constants of the tube coupling circuits, the potential on the grid of the other tube increases sufiiciently to cause a current fiow energizing the switching device in its anode-cathode discharge path, which is effective to shift the first tube to a low potential.

To vary the coupling circuit time constants, impedance means are connected between the input circuits of the two tubes and joined by an adjustable element to a low potential, whereby variation of the adjustable element to change the impedance effectively in the tube input circuits will change the pulse width generated by the multivibrator without interfering with the recurrence frequency, because the combined time constant is not varied.

These and further advantages of the invention will be more readily understood when the following description is read in connection with the accompanying drawings, in which:

Figure l is a schematic circuit diagram of a multivibrator in accordance with the principles of the present invention; and

Figure 2 is a schematic circuit diagram of a modified 2,880,322 Patented Mar. 31, 1959 multivibrator in accordance with the present invention which provides both independent pulse width and recurrence frequency controls.

Referring to an illustrative embodiment of the present invention in greater detail with particular reference to Figure l, vacuum tubes 1 and 2, shown as triodes but which may include further electrodes, have their cathodes returned to ground and their anodes coupled through respective relay windings 3 and 4 to a source of positive potential. An armature 3a of the relay 3, normally joined to the positive source and movable to a grounded terminal, is connected through a capacitor 5 to the tube 2 control grid, which is also coupled through a resistor 6 to one end of a variable potentiometer 7. A slidable tap 7a grounds the potentiometer. In similar fashion, an armature 4a, movable between the positive source and ground, is coupled by a capacitor 8 to the tube 1 grid, which is also coupled by a resistor 9 to the other side of the potentiometer 7.

in operation, assuming that the circuit is energized with the relays 3 and 4 in the positions indicated thus charging the capacitors 5 and 8, both of the tubes 1 and 2 initially conduct current. Since the characteristics of any tubes differ slightly, the rate of increase of current through one of the tubes will exceed that through the other until the current in one tube, assumed to be tube 1, attains a value suificient to pick up the relay 3. At this time, the potential on the grid of tube 2 suddenly drops and the current fiow therethrough is reduced to a low value insufficient to energize the relay 4. The capacitor 5 now discharges through a path including the resistor 6 and potentiometer 7 to ground and the potential on the grid of the tube 2 begins to rise, re sulting in an increase in current therethrough. Finally, the tube 2 conducts enough current to energize the relay 4-, whereby the grid of the tube 1 is suddenly coupled to a low potential by reason of the transfer of the armature 4a to its grounded terminal. in the foregoing manner, the relays 3 and 4 are periodically picked up and released.

It will be observed that adjustment of the potentiometer tap 7a varies the time constant affecting discharge of the grid capacitors 5 and 8 without varying the sum of the discharge periods of these circuits. Accordingly, the relays 3 and 4 are energized and deenergized in accordance with the adjustment of the potentiometer 7. In this manner, the pulse width of the output pulses appearing across multivibrator output terminals, which may comprise one of the armatures 3a and 4a, and ground, can be varied within wide limits without changing the pulse recurrence frequency.

Referring next to Figure 2, a rnultivibrator is illustrated in which the recurrence frequency can be varied independently of the pulse width, and the pulse width varied independently of the recurrence frequency, as demonstrated in connection with Figure 1. The multivibrator of Figure 2 is similar to that illustrated in Figure l, and corresponding elements are identified by like reference characters. In Figure 2, however, the tap 7a of the potentiometer 7, instead of being connected to ground, is connected to one end of a further potentiometer iii and may be coupled through a resistor 11 to the source of positive potential to provide a suitable operating potential. The other end of the potentiometer iii and an adjustable arm 10a are grounded.

With the Figure 2 circuit, the pulse width control of the potentiometer 7 acts in the manner described above; i.e., the time constant in one grid circuit is varied relative to the time constant in the other without changing the sum of the time constants. Adjustment of the potentiometer arm 10a, however, changes the sum of these time a,eso,a22 I constants and varies the recurrence frequency of the multivibrator.

While the relay windings have been connected in the anode circuits of the tubes 1 and 2, it is possible, of course, to connect these windings in the cathode circuits and the operation of the multivibrator will be the same. Moreover, it is apparent that other switches such as electronic switches may be substituted for the mechanical switching arrangement disclosed.

It will be understood that the above-described embodi ments of the invention are illustrative only and modifications thereof will occur to those skilled in the art. Therefore, the invention is not to be limited to the specific apparatus disclosed herein.

' I claimr" l. A free-running multivibrator comprising first and second vacuum tubes each including an anode, a control grid and a cathode, means connecting the first tube in a first series circuit, means connecting the second tube in a second series circuit in parallel with the first series circuit, switching means connected in each of the anodecathode discharge paths, said switching means normally providing at its output one potential and responsive to a selected value of current flow through its associated tube to provide another potential, first capacitance means coupling the first tube input circuit and the output of the switching means in the anode-cathode discharge path of the second tube, second capacitance means coupling the second tube input circuit and the output of the switching means connected in the anode-cathode dis charge path of the first tube, each of the tube input circuits responsive to said one potential to increase current flow in its associated tube and responsive to said other potential to decrease current flow in its associated tube, impedance means connected between the input circuits and said first and second tubes, and adjustable electrically conductive means incorporated in the impedance means to vary the impedance of the input circuits while the impedance between the input circuits remains constant.

2. A multivibrator as defined in claim 1, wherein said electrically conductive means includes means to increase the impedance of the input circuits simultaneously and decrease the impedance of the input circuits simultaneously.

3. A free-running multivibrator comprising first and second vacuum tubes, each tube being provided with a cathode, an anode and a control grid, a relay associated with each tube having a winding and an armature movable between first and second terminals, a first series circuit including the first relay winding and the anode-cathode discharge path of said first tube, a second series circuit shunting said first circuit and including the second relay winding and the anode-cathode discharge path of said second tube, means coupling the first terminals of the relays to a high potential and coupling the second terminals of the relays to a low potential, capacitance means coupling the armature of said first relay to the control grid of said second tube and the armature of said second relay to the control grid of said first tube, a potentiometer connected at one end to the grid of said first tube and at the other end to the grid of said second tube, and a tap on said potentiometer connected in circuit with the first and second series circuits to vary the impedance of the input circuits while the impedance between the input circuits remains constant.

4. The combination as set forth in claim 3, wherein each of the armatures engages the first terminal when said relay is deenergized and engages the second terminal when said relay is energized.

5. The combination as set forth in claim 3, wherein the relay winding of each series circuit is connected between the first potential and the anode of the tube in said series circuit.

6. A free-running multivibrator comprising first and second vacuum tubes, each tube being provided with an anode, a cathode and a control grid, an electric device associated with each tube provided with an output electrode and characterized by a first electric state in which said electrode is connected to a high potential and a second electric state in which said electrode is connected to a low potential, means connecting the anode-cathode discharge path of said first tube in series with said first device to form a first series circuit, means connecting the anode-cathode discharge path of said second tube in series with said second device to form a second series circuit in parallel with said first series circuit, first capacitance means coupled between the electrode of said first device and the grid of said second tube, second capacitance means coupled between the electrode of said second device and the grid of said first tube, impedance means connected between the grids of said first and second tubes, and adjustable electrically conductive means incorporated in the impedance means to vary the impedance of the control grids while the impedance between the control grids remains constant.

7. The combination as set forth in claim 6, wherein each device attains said first state when the current flow in the corresponding series circuit attains a predetermined value and attains said second state when said current flow falls below said value.

8. A multivibrator as defined in claim 6, wherein the electrically conductive means includes a potentiometer to vary the impedance of the input circuits while the impedance between the input circuits remains constant.

9. In combination, first and second vacuum tubes, each tube being provided with a cathode, an anode and a control grid, a relay associated with each tube having a winding and an armature movable between first and second terminals, a first series circuit including the first relay winding and the anode-cathode discharge path of said first tube, a second series circuit shunting said first circuit and including the second relay winding and the anode-cathode discharge path of said second tube, means coupling the first terminals of the relays to a high potential and coupling the second terminals of the relays to a low potential, capacitance means coupling the armature of said first relay to the control grid of said second tube and coupling the armature of said second relay to the control grid of said first tube, first and second variable potentiometers having adjustable taps, said first potentiometer being connected at one end to the grid of the first tube and at the other end to the grid of the second tube, said second potentiometer being connected at one end to the tap of the first potentiometer and at the other end in circuit with the first and second series circuits, the tap of said second potentiometer being con nected in circuit with the first and second series circuits, and means to energize the tap of said first potentiometer independently of the first and second potentiometers.

References Cited in the file of this patent UNITED STATES PATENTS UNITED STATES PATENT OFF-ICE CERTIFICATE OF CORRECTION Patent No; 2,880,322 March 31, 1959 William W. Saks It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as' corrected below.

Column 1, line 53, after "tube insert grid Signed and sealed this 14th day of July 1959.

(SEAL) Attest:

A j ROBERT c. wATsor Attest ng- Officer Comnissioner of Patent UNITED STATES PATENT OFF-ICE CERTIFICATE OF CORRECTION Patent No." 2,880,322 March. 31, 1959 William w. Saks It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 53, after "tube" insert grid Signed and sealed this 14th day of July 1959.

Attest:

AXLINE Attest ng; Officer ROBERT C. WATSOh Commissioner of Patent: 

